Induction meter having magnetically supported rotor



Nov. 26, 1968 wR| 5HT 3,413,550

INDUCTION METER HAVING MAGNETICALLY-SUPPORTED ROTOR Original Filed Feb.26, 1960 2 Sheets-Sheet l INVENTOR David E Wright ATTORNEY D. F. WRIGHT3,413,550

INDUCTION METER HAVING MAGNETICALLY-SUPPORTED ROTOR Nov. 26, 1968 2Sheets-Sheet 2 Original Filed Feb. 26, 1960 H- Demognetizofion ForceUnited States Patent 3 413,550 INDUCTION METER HAVING MAGNETICALLY-SUPPORTED ROTOR David F. Wright, Raleigh, N.C., assignor to WestinghouseElectric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania Original application Feb. 26, 1960, Ser. No. 11,335, nowPatent No. 3,143,704, dated Aug. 4, 1964. Divided and this applicationMay 26, 1964, Ser. No. 370,168

2 Claims. (Cl. 324-152) ABSTRACT OF THE DISCLOSURE An induction meterhas a rotatable electroconductive armature and two damping magnet fieldswhich vary in cross-section oppositely in a direction parallel to thearmature axis.

This application is a division of my patent application Ser. No. 11,335,filed Feb. 26, 1960, now Patent 3,143,704.

This invention relates to rotatable structures and has particularrelation to mechanisms for magnetically supporting a rotor for rotationabout a vertical axis.

It has been heretofore proposed that a rotor be magnetically supportedfor rotation. According to one proposal two magnets are employed inattraction for this purpose. According to a second proposal two magnetsare employed in repulsion for the same purpose.

In accordance with the invention, two permanent magnets are employed forsupporting a rotor for rotation about a vertical axis. The magnetsdesirably have coercive forces in excess of 1000 oersteds and preferablyin excess of 1200 oersteds. Magnets of the ceramic or ferrite type areparticularly suitable. Such material may have the chemical compositionMO.6Fe O wherein M may represent barium, strontium or lead. Materialhaving the composition BaO.6Fe O is commercially available and issatisfactory. Such a magnet may have a coercive force in excess of 1500oersteds and has excellent resistance to corrosion.

In a preferred embodiment of the invention, each of the ferrite magnetsis provided with a pair of circular poles of different diameters whichare concentric relative to the axis of rotation of the rotor unit. Eachof the magnets preferably is ring-shaped and is magnetized in an axialdirection. The magnet is located within a cup-shaped member of softmagnetic material, the rim of the cup constituting one of the poles ofthe magnet. Two of these cup-shaped magnetic members are positioned withtheir open ends adjacent each other and in axial alignment. The magnetscontained within the members are magnetized to provide like polesadjacent each other in order to produce a repulsion effect.

The provision of the cup-shaped members has several favorable effects.Not only is the efficiency of the magnetic mounting materially improved,but the effect of temperature variations on the repulsion force can bematerially reduced. The cup-shaped members are readily machined toprovide accurate cylindrical surfaces which minimize any magneticirregularities due to structural defects of the magnets. The magneticmembers provide some shielding for the permanent magnets andconsequently reduce external field influence on the permanent magnets byreducing the interaction between the magnet leakage field and anyexternal fields which may be present adjacent the mounting. Thecup-shaped members produce large supporting fields which aresubstantially less sensitive to the axial position of the rotor unit.The cupice shaped member additionally facilitates the holding of theassociated permanent magnet and provides good mechanical protection forsuch magnet.

In a preferred embodiment of the invention resilient pins are providedto locate the rotor unit accurately with respect to its axis ofrotation. In one embodiment of the invention, one of the pins may havean electroconductive disc secured thereto and positioned in the field ofone of the magnets employed for the mounting. Movement of the pin withrespect to the magnet induces eddy currents in the disc and consequentlydamps such movement of the pm.

In an embodiment of the invention, the rotor unit may include anelectroconductive disc which is located in the air gaps of dampingmagnets. Such magnets provide magnetic fields for the electroconductivedisc and act to damp orretard rotation of the disc by a retarding forcewhich is proportional to the rate of rotation of the disc. Preferably,such damping magnets provide a resultant magnetic field for the discwhich is virtually the same for all positions which the disc may occupyin a direction parallel to the axis of rotation of the disc. If one ofthe damping magnets provides an air gap field which varies from point topoint in a direction parallel to the axis of rotation, a second clampingmagnet preferably is provided which has a magnetic field tending tocompensate for the magnetic field variations of the first magnet.

It is therefore an object of the invention to provide an improvedmagnetic mounting for a rotor unit which is designed for rotation abouta vertical axis.

It is also an object of the invention to provide an improvedconstruction of a damping magnet assembly for damping rotation of arotor.

Other objects of the invention will be apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich;

FIGURE 1 is a view in front elevation with parts broken away of awatt-hour meter having a magnetic mounting embodying the invention;

FIG. 2 is a view in side elevation with parts broken away showing therotor assembly and associated parts of a watt-hour meter of FIG. 1;

FIG. 3 is a view in side elevation of a prior art magnetic mountingshowing magnetic field lines of the suspension diagrammatically;

FIG. 4 is a view in sectional elevation of the magnetic mounting of FIG.1 with parts broken away and with magnetic field lines diagrammaticallyshown;

FIGS. 5 and 6 are views in perspective of damping magnets which may beemployed in place of the damping magnets shown in FIG. 1;

FIG. 7 is a graph showing various operating points on thedemagnetization curve of a permanent magnet;

FIG. 8 is a view in sectional elevation with parts broken away showing amodified magnetic mounting; and

FIG. 9 is a perspective view of a modified form of magnetic mountingwith parts broken away.

Referring to the drawing, FIG. 1 shows an alternatingcurrentinduction-type watt-hour meter 1 located within a conventional casingwhich includes a base 3 and a cupshaped glass cover 5. The watt-hourmeter has a stator unit which includes an electromagnet of substantiallyconventional construction. In the specific embodiment of FIG. 1, theelectromagnet includes a magnetic structure 7 having a voltage section 9and a current section 11 which are separately constructed and secured toeach other. The voltage section 9 includes a voltage pole 9A having avoltage winding 9B positioned to direct magnetic flux through thevoltage pole. As is well understood in the art, the voltage winding 9Bhas a large number of turns of conductor having a small cross-section.

The current section 11 of the magnetic structure has two current poles11A and 118 which respectively have windings 11C and 11D associatedtherewith. In accordance with customary practice, the windings 11C and11D have a relatively small number of turns of electric conductormaterial having a large cross-section and are energized in accordancewith current flowing in an electrical circuit with which the watt-hourmeter is associated. The current windings are so associated with thecurrent poles that when the winding 11C directs magnetic flux upwardlyin the pole 11A, the winding 11D directs current magnetic fluxdownwardly in the pole 11B.

The poles 9A, 11A and 11B are spaced to provide an air gap in which anelectroconductive disc 13 is mounted for rotation. It will be understoodthat when the voltage winding 9B is energized in accordance with thevoltage of an alternating-current circuit and the windings 11C and 11Dare energized in accordance with current flowing in thealternating-current circuit a shifting magnetic field is established inthe air gap containing the disc 13. This shifting magnetic field resultsin the application of a torque acting between the disc or armature 13and the electromagnet to produce rotation of the disc. This torque isproportional to the power flowing in the associated alternating currentcircuit.

The electroconductive disc or armature 13 is mounted for rotation abouta vertical axis on a shaft 15. This shaft cooperates with anupper-bearing assembly 17 and a lower-bearing assembly 19 to mount thedisc 13 for rotation with respect to the electromagnet. Theupper-bearing assembly 17 is secured to the electromagnet in anysuitable manner as by means of a frame 21 and a set screw 23. In ananalogous manner, the lower bearing assembly 19 is positioned by theframe 21 and by a set screw 25.

In order to damp rotation of the disc 13, one or more damping magnetsmay be employed. In the embodiment of FIG. 1, two damping magnets 27 and29 have air gaps within which the disc 13 is mounted for rotation.Consequently, the damping magnets retard rotation of the disc 13 with aforce or torque which is dependent on the rate of rotation of the disc.

As shown more clearly in FIG. 2, the disc 13 is secured to the shaft inany suitable manner. In a preferred embodiment of the invention, thedisc 13 is provided with an opening through which the shaft 15 extends.A hub of die-casting material 31 is then formed about the shaft and disccenter in order to hold the two parts together. The upper portion of thehub may be contoured to provide a ratchet wheel 33 havingupwardlydirected ratchet teeth. This ratchet wheel may be associatedwith a pawl to prevent reverse rotation of the disc 13 as set forth inthe copending Tringali application, Ser. No. 763,732, filed Sept. 26,1958, now abandoned. The shaft 15 may be constructed of a suitablematerial such as aluminum and may have teeth cut therein to form a worm35 which cooperates with a worm wheel 37. The

worm wheel 37 forms part of the conventional register which is driven bythe shaft 15 to register energy consumed by an alternating-currentelectrical circuit with which the watt-hour meter is associated.

In order to guide the upper end of the shaft 15, the upper end isprovided with a cup-shaped recess 38 for receiving a suitable ringbearing 39. This ring bearing is constructed of a suitable material suchas bronze or sapphire which is held in position in the shaft 15 in anysuitable manner as by a staking or a spinning operation. Preferably thering bearing 39 is constructed of graphite.

The upper bearing assembly 17 includes a pin 41 which has its upper endsecured to a surrounding sleeve 43 in any suitable manner as by means ofa die-casting alloy 45. The lower end of the pin 41 extends through thering bearing 39 to locate the upper end of the shaft on its axis ofrotation. In order to minimize the transmission of vibration and noisebetween the rotor and stator units, the pin 41 is constructed of aresilient material such as stainless steel and has a substantial lengthbetween the ring bearing 39 and the point of attachment of the pin tothe sleeve 43.

In an analogous manner, the lower end of the shaft 15 is provided with aring bearing 47. The lower bearing assembly 19 includes a pin 49 whichis secured to a sleeve 51 and which extends through the ring bearing 47.The'pin 49 corresponds to the pin 41 of the upperbearing assembly.

In order to support the weight of the rotor unit which includes thedisc13, the shaft 15 and associated parts, two permanent magnets 53 and 55are mounted concentric with the axis of rotation of the rotor assembly.The permanent magnet 53 is secured to the stator unit whereas the magnet55 is secured to the rotor unit. The permanent magnets are magnetizedaxially in such directions as to present like poles adjacent to eachother. For exemplary purposes, it assumed that the permanent magnet 53is magnetized to provide an upper north pole and a lower south poleindicated in FIG. 2 respectively by the reference characters N and S. Inan analogous manner, the upper permanent magnet 55 is provided with alower north pole and an upper south pole. As a result of thesemagnetizations, the permanent magnets develop a repulsion force which issuflicient to support the weight of the rotor assembly. Consequently,the only friction present in the system is that between the pins 41 and49 and their associated ring bearings 39 and 47.

The permanent magnets 53 and 55 preferably are constructed of a materialhaving a high coercive force. Excellent results have been obtained frommaterials known as ceramic or ferrite permanent magnet materials. Such amaterial may have a chemical formula MO 6Fe O wherein M represents amaterial such as barium, lead or strontium, Fe represents iron and 0represents oxygen. In a preferred embodiment of the invention, thebarium-containing material is employed and is represented by thechemical formula BaO-6Fe O Such a material may have a coercive force inexcess of 1000 oersteds and material having a coercive force of theorder of 1600 oersteds has been employed.

Although the parameters of the permanent magnet material depend on thespecific rotor to be supported the following dimensions have been foundsuitable for a watthour meter. Each of the permanent magnets 53 and 55is constructed of a barium ferrite in the form of a ring. The ring hasan outer diameter of 0.270 inch, an inner diameter of 0.140 inch and anaxial length of 0.125 inch. The weight of such a permanent magnet isonly 0.40 gram.

As employed in a repulsion permanent-magnet system, the ceramic materialoffers extremely high resistance to both self and externaldemagnetization. Furthermore, the material is extremely stable andnon-corrosive.

Although the permanent magnets 53 and 55 may be employed withoutprovision of other magnetic material in the mounting, a number ofimportant advantages are obtained by reducing the air gaps of thepermanent magnets. To this end, each of the permanent magnets 53 and 55is asociated with a soft magnetic cup.

As shown in FIG. 2, the permanent magnet 53 is located in a cup 57constructed of a soft magnetic material such as a low-carbon steel orcold-rolled steel. For a permanent magnet 53 having the dimensionspreviously given, the cup 57 may have a cylindrical wall portion with aninner diameter of 0.320 inch and an outer diameter of 0.344 inch. Thepermanent magnet 53 may be secured to the cup 57 by cement or in anyother suitable manner. In a preferred embodiment of the invention, thepermanent magnet is secured to the cup by means of a solder 59 having amelting point which does not injure the magnet. Such a solder may be ofany suitable composition. For example, it may have a composition byweight of lead 5% tin and 15% antimony. Such material has a meltingpoint of about 275 C. which does not harm the permanent magnet. The cup57 in turn is secured in any suitable manner to the sleeve 51 as bymeans of a press fit. As representative of the suitable material, thesleeve 51 may be constructed of brass.

Preferably the cup 57 is provided with a hollow conical base portion 60concentric about the axis of the shaft 15. This. conical base portion 60rests snugly in a conical seat 60A provided in the sleeve 51 to centerthe cup accurately relative to the sleeve. The conical base portion hasa tubular projection 60B which may have a light knurl on its outersurface and which has a press fit in a cylindrical recess provided inthe sleeve 51.

In an analogous manner, the permanent magnet 55 may be secured within acup 61 which is formed of soft magnetic material similar to thatemployed in the cup 57. It will be assumed that solder 63 is employedfor securing the permanent magnet 55 to the cup 61. The cup in turn maybe secured to the shaft in any suitabl manner, for example, the shaftmay have a portion re ceived as a press fit within a cylindrical openingextending through the central portion of the cup. If desired, the cup 61may be secured to the shaft 15 by a suitable die-casting material 65,such as a lead-base, die-casting material. The cup 61 may have a tubularprojection 61A of reduced diameter provided with a groove 61B in itsouter surface. The shaft 15 may have grooves 15A formed therein. Thegrooves provide interlocks between the material 65 and the projection61A and the shaft 15.

By inspection of FIG. 2 it will be noted that the sleeve 51 has atubular projection 51A which surrounds not only the cup 57 but asubstantial part of the cup 61. Thus the projection 51A affords physicalprotection for the cups and for the air gap between the cups. Because ofits non-magnetic construction the projection 51A can extend close to theair gap for maximum physical protection.

Because of the presence of the cup, the north pole face of each of thepermanent magnets is in effect surrounded by a concentric south poleface, the two pole faces being coupled to each other through anefficient magnetic circuit. The soft steel cup then constitutes a fluxreturn path which materially increases-the magnetic flux available forlift of the rotor unit.

Furthermore, the cups are constructed of a readily rnachi-nable materialand consequently can be provided with extremely accurate concentricoutside diameters. This is desirable in order to minimize radial forcesacting between the rotor assembly and the stator. Furthermore, theprovision of cups facilitates the utilization of permanent magnets 53and 55 having imperfections such as chips therein. When brittlepermanent-magnet material such as the ceramic materials are employed, itis desirable to permit the utilization of chipped permanent-magnetmaterial.

The cups also provide a measure of shielding for the permanent magnetsand decrease the likelihood of interaction between the permanent-magnetfields and the electro-magnet.

It has been found further that the cups materially reduce the effect ofambient temperature variations on the position of the rotor unit. As theambient temperature increases, the magnetization of the ferritedecreases. This tends to cause the rotor unit to drop slightly. Tocompensate for this drop, the cups 57 and 61 may be constructed of amaterial having a magnetic permeability which increases withtemperature. With the low-carbon steel cups mentioned above it has beenfound possible to decrease the reversible change in displacement of therotor unit over a temperature range of 40 C. to 55 C. by almost 60%.When the temperature departs from an initial value the rotor unitposition may change slightly. However, when the temperature returns toits initial value the rotor unit also returns to its initial position.

The advantages flowing from the provision of the soft magnetic cups forthe permanent magnets may be considered further by reference to FIGS. 3and 4. FIG. 3

represents two permanent magnets heretofore proposed for a magneticmounting. The permanent magnets are magnetized to provide poles asindicated by the polarity markings N for north pole and S for southpole. The magnetic fields F for these two permanent magnets are plottedin FIG. 3. An extremely large leakage field is present.

In FIG. 4, a field is shown for the magnetic mounting of FIGS. 1 and 2.It will be observed that the leakage field is materially reduced and themagnetic field is concentrated to a large extent in the gap between thetwo cups. Not only is the efficiency of the magnetic mounting materiallyimproved, but a flat magnetic field configuration is obtained whichmakes the magnetic mounting less responsive to the radial displacementof the rotor unit from its correct position.

FIG. 7 shows a demagnetization curve A for the ferrite permanent magnet53 plotted in the customary manner with ordinates B representinginduction usually measured in gausses and abscissae H representingdemagnetizing force, usually measured in oersteds.

The ferrite magnet 53 alone has an operating point determined by theintersection of a line C with the demagnetization curve A.

If the ferrite magnet 53 is placed in its cup 57, the operating point isrepresented by the intersection of a line D with the demagnetizationcurve A. When the magnet 53 and its cup 57 are in the complete mountingas shown in FIGS. 1 and 2 the operating point is represented by theintersection of a line B with the demagnetization curve A.

In FIG. 1, it is assumed that each of the permanent magnets 27 and 29has pole faces of equal size and shape on opposite sides of the disc 13.With this assumption, displacement of the disc 13 in a verticaldirection from the position illustrated in FIG. 1 has little effect onthe damping provided by the damping magnets 27 and 29.

In some cases, it is desirable to provide an adjustable pole piece forat least one of the damping magnets. Such a pole piece 27B is associatedwith a permanent magnet 27A in FIG. 5 which may be employed in place ofthe permanent magnet 27 of FIG. 1. Because of the pole piece 27Bprovided on the lower pole face of the magnet 27A, the damping torqueproduced by the damping magnet 27A depends to some extent on thevertical position of the disc in the air gap of the magnet.

If the damping magnet 27A of FIG. 5 is employed in place of the dampingmagnet 27 of FIG. 1, the watthour meter may be made substantiallyindependent of the vertical position of the rotor assembly by replacingthe damping magnet 29 of FIG. 1 by the damping magnet 29A of FIG. 6-.

As shown in FIG. 6, the permanent magnet 29A has a pole piece 29Bsecured to the upper pole face of the damping magnet. Thus, as the discmoves upwardly, the area of the field produced by the magnet 27A whichis cut by the disc decreases whereas the area of the field produced bythe magnet 29A which is cut by the disc increases. Because of theseopposite variations in the two fields, the damping of the disc isvirtually independent of its vertical position.

The construction shown in FIGS. 1 and 2 has been found to provideeffective performance. However, if it is desirable to damp radialvibration of the rotor unit, the pin 49 may have mounted thereon anelectroconductive disc 81 (FIG. 8) such as a copper disc. The remainingparts of FIG. 8 are similar to those of FIGS. 1 and 2 except for aslightly greater spacing between the cups 57 and 61 to provide adequatespace for the disc 81, and except for a permanent magnet 53A whichdiffers from the permanent magnet 53 of FIGS. 1 and 2 only in its innerdiameter.

Radial vibration of the rotor unit tends to move the pin 49 and the disc81 mounted thereon in a radial direction. Such movement causes the disc81 to cut magnetic flux produced by the magnet 53A. Consequently, eddycurrents are induced in the disc 81 and produce forces 7 which oppose ordamp the vibration which cause the movement of the disc.

The inner diameter of the magnet 53 of FIGS. 1 and 2 may be reducedmaterially with a resultant increase in .efliciency, with no increase inouter dimensions and with no increase in weight of the rotor unit. Thisis illustrated in FIG. 8 wherein the magnet 53A has an inner diametermerely large enough to provide running clearance for the pin 49. As aspecific example, the inner diameter may be 0.063 inch.

By reference to FIG. 1, it will be noted that the magnets employed inthe bearing assembly 19 are spaced appreciably from the cover 5. In awatt-hour meter as actually constructed, it was impossible to bring ademagnetizing coil closer than 2% inches to the magnets 53 and 55.Although the ceramic magnets are extremely resistant to demagnetization,the increased spacing available in the design of FIG. 1, is alsoeffective in preventing demagnetization of magnetic materials used inthe bearing system.

In the bearing systems previously discussed, permanent magnets areemployed in repulsion and ceramic magnets are particularly desirable forsuch applications. However, ceramic magnets also are desirable forattraction-type suspension systems. For example, let it be assumed thatthe watt-hour meter of FIGS. 1 and 2 has an attraction suspensionassociated with the upper bearing assembly, as illustrated in FIG. 9.

In FIG. 9, a permanent magnet 91 is secured to the upper end of theshaft 15. This permanent magnet is surrounded by a tubular permanentmagnet 93 which is fixed to the stator. The two permanent magnets aremagnetized in axial directions to provide poles as indicated by themarkings N for north pole and S for south pole. By inspection of FIG. 9,it will be observed that forces of attraction operate between the twopermanent magnets to suspend or support the rotor unit associated withthe shaft 15. Such a construction is well known in the art.

In accordance with the further aspect of the invention, the two magnets91 and 93 are constructed of the ceramic materials previously described.

Although the invention has been described with reference to certainspecific embodiments thereof, numerous modifications falling within thespirit and scope of the invention are possible.

I claim as my invention:

1. In combination: a stator unit, a rotor unit, means mounting the rotorunit for rotation relative to the stator unit about a verical axis, saidrotor unit having an operating position relative to the stator unitwhich may vary over a range along said vertical axis, one of said unitscomprising an air-gap-containing magnetic means having a magnetic fieldtherein and the other of said units comprising an electroconductingarmature having a portion positioned in the magnetic field to developdamping torque acting between the units in response to relative rotationof said units about said vertical axis, said magnetic means providing amagnetic field proportioned to develop a damping torque acting betweenthe units which is independent of the vertical position of said rotorunit relative to the stator unit over said range, the armaturecomprising a disc concentric about the axis, and the magnetic meanscomprising a first permanent magnet unit providing .a first magneticfield portion and a second permanent magnet unit providing a secondmagnetic field portion, said first magnetic field portion having ahorizontal cross-section which increases in a first vertical direction,and said second magnetic field portion having a horizontal cross-sectionwhich decreases in said first vertical direction, each of said permanentmagnet units comprising -a C-shaped permanent magnet having pole faceson opposite sides of said disc, each of the permanent magnets having afirst pole face which is substantially larger than its other pole face,the first pole faces of said two permanent magnet units being onopposite sides of said disc.

2. The invention claimed in claim 1 wherein one of said permanentmagnets comprises a pole piece providing the larger of said pole faceswhich is adjustable for varying the magnitude of the associatedmag-netic field portion.

References Cited UNITED STATES PATENTS 1,332,464 3/1920 Harris 324-1522,254,698 8/1941 Hansen 324 155 X FOREIGN PATENTS 717,660 10/1954 GreatBritain.

RUDOLPH V. ROLINEC, Primary Examiner.

G. R. STRECKER, Assistant Examiner.

